Embodiments of the invention relate generally to magnetoresistive random access memory (MRAM) and, more specifically to thermally-assisted MRAM having cavities adjacent to tunnel junctions.
Magnetoresistive random access memory (MRAM) is a non-volatile computer memory (NVRAM) technology. Unlike conventional RAM chip technologies, MRAM data is not stored as electric charge or current flows, but by magnetic storage elements. The elements are formed from two ferromagnetic plates, each of which can hold a magnetic field, separated by a thin insulating layer. One of the two plates is a reference magnet set to a particular polarity; the other plate's field can be changed to match that of an external field to store memory and is termed the “free magnet” or “free-layer”. The free magnet may also be referred to as a bit, and it may store a “1” or a “0” value. This configuration is known as a magnetic tunnel junction and is the simplest structure for a MRAM bit. A memory device is built from a grid of such “cells.”
One type of MRAM, called thermal MRAM, is configured to have heat applied to the tunnel junction when writing to a bit of the tunnel junction. In particular, the free magnet tends to be stable at a normal operating temperature, and it is more difficult to change magnetic polarity of the free magnet at a normal operating temperature. Providing heat to the free magnet may facilitate changing of a polarity of the free magnet to program a magnetic state of the free magnet. However, heat generated by the current flowing through the tunnel junction may be lost in surrounding insulating or dielectric layers, requiring an increase in current to generate a desired amount of heat in the tunnel junction.